There are a multitude of different gas valves available for use in semiconductor process control. The following valves and related flow control devices are used in circumstances where the amount of gas to be delivered is very small (at the micro or even nano mass level).
Vacuum leak valves (sometimes referred to as a type of vacuum throttle valve) are widely used for controlling the flow of gases at very low pressures. A typical leak valve comprises a knife edge seal and is actuated by controlling the pressure applied to a metal diaphragm. Commonly, the actuator is a finely threaded screw in the valve body which applies pressure to the metal diaphragm. (A variable leak valve of this type is available from MDC Vacuum Products, LLC as part number 315002.) Other vacuum leak valves comprise an optically flat sapphire that meets a captured metal gasket to form the seal. The pressure with which the sapphire is held against the gasket is controlled by a movable piston attached to a lever arm mechanism with a mechanical advantage of the order of 10,000 to 1. (A variable leak valve of this type is available from Varian, Inc. as part number 9515106.) The actuator may be manual or computer controlled.
A mass flow controller (MFC) is a device used to measure and control the flow of gas using flow sensors and valves. Proportional valves are often used in MFCs. A proportional valve typically comprises a proportional solenoid or an on/off solenoid operated in a dithering mode. However, MFCs are only available for gas flow control down to the micro mass level, and not for nano mass flow control.
A gas pressure regulator is a valve that automatically stops the flow of gas when a preset pressure is reached on the output side of the valve. A regulator is often installed between the gas source (such as a cylinder of compressed gas) and a MFC or a leak valve (which controls the flow of gas into a process chamber).
For processes such as atomic layer deposition, a controlled pulsed delivery of precursor gases at the micro and nano mass levels will be advantageous.
Therefore, there remains a need in the semiconductor industry for a means of precisely controlling the flow of gases and for delivering gas at micro and even nanobar mass levels. Furthermore, there remains a need for a means of providing a pulsed delivery of gases at micro and nanobar partial pressures.